1. Field of the Invention
The current invention relates to sensing elements and devices comprising at least one amphipathic lipid-binding protein or fatty acid binding protein, wherein the binding proteins are associated with a luminescent reporter group. The binding proteins and luminescent reporter groups are encapsulated within a hydrogel matrix that comprises at least one co-monomer, wherein the co-monomer is present at a concentration that decreases or inhibits micelle formation of the amphipathic lipid. Binding of the amphipathic lipid or fatty acid to the appropriate binding protein can produce at least one detectable change in the property of the luminescent reporter group.
2. Background of the Invention
Recent studies have shown that elevated free fatty acid (FFA) levels have a negative impact on human health. Individuals with FFA levels significantly higher than those of the general population are at increased risk of mortality, heart disease and insulin resistance, a hallmark of type 2 diabetes. Despite these relationships, FFA levels are not monitored by physicians nearly as routinely as other analytes such as cholesterol, triglycerides and glucose. One obstacle to FFA joining this panel of routinely tested species is the method of quantification. The two most commonly used approaches involve either the use of radiolabeled reagents with complex instrumentation, or an enzyme-based colorimetric assay requiring strict time and temperature controls. Neither approach is ideal in a point-of-care setting. Knudsen and co-workers recently described an alternative approach using enzymatic modification and a fluorescently labeled binding protein, but this method still requires complex sample handling and has a slow (>1 hour) turnaround time.
The limitation of acrylodan-labeled fatty acid binding protein is that the CMC (critical micelle concentration) of fatty acids occurs at ˜75 μM. At fatty acid concentrations above the CMC, the concentration of free fatty acid remains essentially constant. Because acrylodan-labeled fatty acid binding protein only measures monomeric free fatty acid, the CMC places an upper limit on the measurable fatty acid content in a sample. Higher concentrations can only be quantified following dilution of biological samples. Clearly there exists a need, particularly for in vivo monitoring, for a biosensor that can directly measure fatty acids in samples without the need for dilution.